A vapor exchange medium is basically a desiccant or molecular sieve that may be used to remove water vapor from the ambient air. For example, desiccants such a silica gel and alumina gel, in powder form, are commonly used to minimize the moisture content of the air in containers housing objects that could be damaged by such moisture. The powder particles contain minute pores which enable the particles to adsorb water vapor present in the air inside the package. If the desiccant is then removed from the package and regenerated by placing it in a dry atmosphere, e.g., a heated oven, the particles will release or desorb the water vapor into that environment.
On a much larger scale, a desiccant may be incorporated into the heat exchange wheel of a heat exchanger so that that apparatus functions as a heat/moisture exchanger. A typical such wheel comprises web material carrying a desiccant and spirally wound into a roll or wheel, with the adjacent convolutions of the rolled web being spaced apart, e.g., by web corrugations, so that air can travel axially along the wheel. The wheel may be rotatably mounted coaxially in a duct which is divided in half lengthwise by a partition so that the wheel intercepts both halves of the duct. If hot, humid air is moving along one half of the duct, say, into an air conditioned building, and cooler, dryer air being exhausted from the building is traveling through the other half of the duct, rotation of the wheel will transfer heat and moisture from the incoming air to the outgoing air. In other words, at any given time, the sector of the wheel that intercepts the half of the duct carrying the incoming air will absorb heat and adsorb water vapor from that air. When that sector of the wheel rotates opposite the half of the duct passing the outgoing air, the wheel portion will give up heat and moisture to that cooler, dryer air. Thus, as the wheel rotates, the desiccant in progressive sectors of the wheel is first adsorbing and then desorbing water vapor. Conventional vapor exchange media and heat exchange wheels formed thereby are described, for example, in U.S. Pat. Nos. 4,391,667; 4,595,403; 4,875,520 and 5,052,188. For simplicity, we will hereinafter refer to such heat/moisture wheels simply as heat exchange wheels or devices.
While prior desiccants function satisfactorily in powder form, when combined with a binder to form a solid structure, they do not display the moisture adsorbing capabilities that would be expected from the amount of desiccant present. In some cases, the desiccant may have a high adsorption affinity for the binder material, be it an organic binder such as latex, or an inorganic binder such as water glass or solutions of water soluble glasses. Resultantly, the binder reduces the capacity of the desiccant particles for water vapor adsorption. Also, some binders contact the desiccant particles over relatively large surface areas thereby occluding the particles pores which degrades the performance of the desiccant.
Further, such vapor exchange media that use organic binders are disadvantaged too because they cannot be used in some regenerative heat exchangers because the heat of regeneration, which may be as high as 450.degree. F., can cause those organic materials to break down.
Those heat exchange devices that incorporate corrugated heat exchange elements suffer because the desiccant is added to the heat exchange elements after the corrugations are formed in those elements. This may reduce the amount of desiccant that can be incorporated into the finished product and also places constraints on the desiccant application equipment which then has to accommodate the unwieldy shape of the corrugated web.
Other prior heat exchange devices and wheels are disadvantaged because they require to many process steps in their manufacture and are thus too cost intensive.
Accordingly, it is an object of the present invention to provide an improved vapor exchange medium which can be configured easily into a solid shape.
Another object of the invention is to provide a medium of this type which is able to withstand the relatively high temperatures commonly used to regenerate the medium.
A further object of the invention is to provide a vapor exchange medium of this generally type which can be incorporated into a heat exchange element.
Yet another object of the invention is to provide a heat exchange device, e.g., a heat exchange wheel, utilizing such a medium.
Yet another object is to provide a vapor exchange element with a variably modifiable geometry.
Another important object of the invention is to provide a heat exchange element having an optimal isotherm separation factor of about 0.07 to 0.1.
A further object of the invention is to provide a method of making a vapor exchange medium and a heat exchange element incorporating such a medium.
Still another object of the invention is to provide a method of making a heat exchange device having one or more of the above advantages.
Still another object of the invention is to provide apparatus for making the aforementioned heat exchange device.
Other objects will, in part, be obvious and will, in part, appear hereinafter.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, the apparatus embodying the features of construction, combination of elements and arrangement of parts which are adapted to effect such steps and the article which possesses the characteristics, properties and relation of elements, all as exemplified in the detailed disclosure set forth hereinafter, and the scope of the invention will be indicated in the claims.